adds Gemfile.lock (#2664)

Makes sure the tests are ran with a working charlock_holmes gem

e.g. prevents this from happening:

https://github.com/brianmario/charlock_holmes/issues/78

Gemfile.lock

@@ -0,0 +1,15 @@
+GEM
+  remote: http://rubygems.org/
+  specs:
+    charlock_holmes (0.7.3)
+    rake (12.0.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  charlock_holmes
+  rake
+
+BUNDLED WITH
+   1.13.7